1. Field of the Invention
This application is directed to an improved method of preparing propane sulfonates. Propane sulfonates are highly useful as surfactants or surface active agents and having high tolerance for brine makes such agents especially useful in tertiary oil recovery processes.
2. Description of the Prior Art
Propane sulfonates of various amines and polyethoxylated alcohols are known surfactants. However, propane sulfonates of alcohols and thiols have only been prepared in the literature by reaction of alkali metal salts of the alcohols or thiols with propane sultone. This is a convenient high yield laboratory synthesis but is not desirable on a large scale for several reasons. Foremost among them are the fact that (1) such a reaction requires multistep synthesis and purification of propane sultone (2) propane sultone is expensive to purify and its overall yield of 80-90% limits the yield in the preparation of propane sulfonates and (3) propane sultone is a known carcinogen. Therefore processes involving the use of propane sultone must utilize expensive controls to minimize worker exposure and despite such controls its use will always engender some risk of worker exposure. Because of its carcinogenicity all waste products must be carefully treated to ensure no residues remain. This extra care coupled with the expensive synthesis and purification of propane sultone further increases the desire and need for an alternative means of making propane sulfonates.
The preparation of allyl ethers, sulfides, or amines is well known in the literature, however, the use of the two step procedure described herein to convert alcohols or thiols to propane sulfonates as far as is known to applicants is unknown. One report appears in the literature of an attempt at a similar process for the preparation of propane sulfonates of tertiary amines [J. Amer. Oil Chem. Soc., 53, 60 (1976)] but it reports the process produces excessive quantities of undesirable "iso-sulfonate" whose presence degrades the performance of the product. This readily demonstrates that the overall conditions we employ are novel and unobvious.
The reaction of MHSO.sub.3 (M is any suitable metal) with simple olefins has been much studied. The literature teaches that for simple water-soluble olefins or olefins which can be made soluble by the addition of small amounts of alcohols all that is required for high conversion to products are conditions in which all reagents are dissolved in a single phase. We find that the allyl-heteroatom compounds do not behave this way. Conditions may be found in which all the reagents are dissolved in a single phase in alcohol and water and yet the conversion will not exceed 40 or 50% unless a minimum amount of sulfonate as disclosed herein is added. When the propane sulfonate is added the conversion is rarely below 90%.
The early literature on the reaction of MHSO.sub.3 with olefins indicated that S-alkylation leading to sulfonate products might be accompanied by a slight amount of O-alkylation leading to sulfites but even this slight formation was disputed and the literature for the last thirty years reveals that sulfites are not by-products in the sulfitation of olefins. We find it surprising that sulfitation of allyl-hetero compounds can produce as great as 100% sulfite in solvents taught in the literature to be acceptable for sulfitation of ordinary olefins to sulfonates. A high yield of sulfite would be surprising because the literature teaches that solvent systems which produce high conversions of olefins will produce high yields of sulfonates.